As researchers gain an increased understanding of the vertebrate immune system, methods to harness and specifically employ the immune system in preventing and fighting of illnesses are constantly being sought. Because of the immune system's extraordinary versatility, this approach—in principle—offers the possibility to react on any substance of sufficient size. Numerous attempts have therefore been made to establish vaccination and/or immunological treatment methods of cancer, bacterial and viral infections.
Such therapy or vaccination methods commonly employ exposing the organism to be treated (in vivo treatment) to vaccine preparations of an antigenic substance, in order to generate an immune response. Particularly, the antigenic substance (antigen) is used to initiate production of immunoglobulins and/or cytotoxic phagocytic cells capable of detecting the antigenic substance itself or parts thereof (epitope), thereby becoming rapidly recognizable to the immune system. An antigen that has such becomes rapidly recognizable and can be inactivated or destroyed, e.g. by uptake into T cells and subsequent disintegration or by destruction of the cells comprising the antigen.
A similar method of vaccination or treatment is to extract lymphocytes—particularly lymphocyte stem cells—from the organism to be treated, exposing the extracted cells to the antigen, thus inducing production of immunoglobulins capable of detecting the antigen, and then reintroducing the immunoglobulin producing lymphocytes into the organism to be treated (ex vivo treatment).
The term “vaccination” denotes treatments of vertebrates primarily to prevent disease or ailment by creating, enhancing or maintaining the immune system's capacity to respond to antigens correlated with the disease or ailment. The term “treatment” denotes creating, enhancing or maintaining the immune system's capacity to respond to antigens correlated with a disease or ailment after the first onset of the disease or ailment, thus being therapeutic in nature. The active ingredient in a vaccination treatment is termed “vaccine”, whereas the active ingredient in a therapeutic treatment is termed “medicament”. The terms “vaccination” and “treatment” are used interchangeably, the same holds for the terms “vaccine” and “medicament”.
One of the most important scientific discoveries of the last ten years has been the definition of tumor associated antigens (TAA) recognized by human T lymphocytes. For reviews see, e.g., Robbins and Kawakami “Human tumor antigens recognized by T cells”, Current Opinion in Immunology 1996, 8:628-636; Rosenberg S A, “A new era for cancer immunotherapy based on the genes that encode cancer antigens”, Immunity 1999, 10:281-287; Van den Eynde B J and van der Bruggen P, “T cell defined tumor antigens”, Current Opinion in Immunology 1997, 9:684-693. The identification and molecular characterization of TAA is widely believed to have provided the means to create cancer vaccines. Current efforts in the creation of such vaccines are based on nucleic acid mediated immunization techniques, i.e. insertion of one or more antigen coding sequences (e.g. a TAA encoding sequence) into suitable expression (host) vectors capable of causing expression of the antigen coding sequence directly within transfected cells. The term “sequence” denotes hereinafter a nucleic acid characterized by the sequence of its nucleotides, wherein a nucleic acid is any molecule comprising one or more nucleotides selected from the group of adenine, guanine, cytosine, thymine, uracil or their functional equivalents like, for example, inosine and hypoxanthine, wherein each nucleobase is linked to a backbone comprising a pentose like ribose and/or deoxyribose, an other sugar or an amino acid, and wherein the individual backbones are linked/connected to one another by, for example, phosphodiester bonding, peptide bonding or other adequate means of linkage/connection. Examples of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Commonly employed host vectors are bacteria and viruses or bacterial and viral genomes, respectively. Recent studies have shown that a cellular or encapsulated vector is not always necessary for vaccine preparation. Immunization with “naked” plasmid DNA and/or with RNA, that is with the nucleic acid being devoid of any other structural components as proteins, lipids, or carbohydrates, can elicit powerful cellular and antibody responses. Nucleic acid vaccines, also termed recombinant vaccines, are thus vaccines in which the genome of the host vector integrates a—frequently heterologous—nucleic acid sequence coding for an immunogen (antigen).
Compared to cell-based vaccines or cell lysates, recombinant vaccines have multiple advantages, the most prominent is probably that they can focus the immune response against a single, specific antigen like a TAA, and thus limit the possibility of releasing an uncontrolled autoimmune aggression against hitherto unknown antigens being present in normal tissues and tumor cells.
Currently vaccination and therapeutic success vary greatly for different ailments and even among patients treated for the same ailment. Furthermore, vaccination does not always last satisfactorily long but can wear off within weeks. These drawbacks hold true also for a number of other vaccination methods, which may in particular involve administration of live or inactivated vaccines. In general, vaccines are not always able to generate an appropriate and effective immune response by themselves.
Certain substances, when administered simultaneously with a specific antigen, will enhance the immune response to that antigen. Such substances (adjuvants) are routinely included in inactivated or purified antigen vaccines. Examples of adjuvants in common use are aluminium salts, liposomes and immunostimulating complexes (ISCOMS), complete and incomplete Freund's adjuvant, muramyl di-peptide and cytokines like interleukin (IL) 2, IL-12 and interferon (IFN) gamma.
Yet, while some adjuvants are well suitable in combination with specific antigens or vaccines, they may fail in other combinations, or they may be toxic themselves to vertebrates like humans, promote poor cell mediated immunity, are unstable or are expensive and/or cumbersome to prepare.
Improved methods for vaccination and treatment of illnesses and ailments in vertebrates are therefore extremely useful.
Another aspect is that for purposes of science, generation of specific cell types e.g. for tissue culture purposes is frequently needed. Among the cell types needed for investigation are dendritic cells and recently discovered fibrocytes.
Dendritic cells are potent antigen presenting cells. They are also reported to act as stimulators of a mixed lymphocyte reaction, to migrate selectively through tissues, to take up, process and present antigens, and serve as passenger cells that elicit rejection of transplanted tissues. For a review see for example Hart D N J “Dendritic cells: unique leukocyte populations which control the primary immune response”, Blood, 1997, 90:3245-3287. Clearly, the study of dendritic cells offers potential applications in any field where the correct recognition of antigens and generation of immune responses is desirable. Such fields are, for example, transplantation medicine, vaccination, therapy of cancer and other illnesses connected with antigen presentation, prevention and treatment of autoimmune diseases and the like, see for example Dallal R M and Lotze M T, “Dendritic cells and human cancer vaccines”, Current Opinion in Immunology, 2000, 12:583-588. However, understanding of dendritic cells and their differentiation is insufficient. It is therefore desirable to have methods for producing dendritic cells.
Current protocols for the production of dendritic cells rely on their differentiation from peripheral blood mononuclear cells, bone marrow cells or other CD34+ cells by exposing such cells to multiple cytokine combinations including granulocyte-macrophage colony stimulating factor (GM-CSF), stem cell factor (SCF), tumor necrosis factor alpha (TNFα), tumor growth factor beta (TGFβ) and IL-4. For a review see for example Strunk D et al., “Generation of human dendritic cells/Langerhans cells from circulating CD34+ hematopoietic progenitor cells”, Blood, 1996, 87:1292-1302 and Soligo D et al., “Expansion of dendritic cells derived from human CD34+ cells in static and continuous perfusion cultures”, British Journal of Hematology, 1998, 101:352-363. Likewise, dendritic cells have been produced from CD14+ blood monocytes and different maturation stages have been described. For a review see Winzler C et al., “Maturation stages of mouse dendritic cells in growth factor-dependent long-term cultures”, Journal of Experimental Medicine, 1997, 185:317-328 and U.S. Pat. No. 6,194,204 B1 by Crawford and Chester. Yet, present protocols rely on expensive and unstable cytokine media components. Likewise, the yield of present protocols for the production of dendritic cells is often considered unsatisfactorily low.
Fibrocytes are a recently described type of cell characterized by their distinct phenotype (collagen+, CD34+), which normally is also vimetin+, CD13+ and CD45+. They are reported to enter rapidly from blood into subcutaneously implanted wound chambers. They are also frequently present in connective tissue scars and may play an important role in wound repair and pathological fibrotic responses. For a review see for example Bucala R et al., “Circulating fibrocytes define a new leukocyte subpopulation that mediates tissue repair”, Mol. Med. 1994, 1:71-81, and Chesney J and Bucala R, “Peripheral blood fibrocytes: novel fibroblast-like cells that present antigen and mediate tissue repair”, Biochemical Society Transactions, 1997, 25:520-4. Like dendritic cells, protocols for the production of fibrocytes rely on expensive and unstable cytokine media components and provide often unsatisfactorily low yields. Therefore, it can be appreciated that there exists a continuing need for new treatments of illnesses and ailments in vertebrates, which can be used to harness and employ the vertebrate immune system in preventing and fighting illness and ailments which remains unsolved by the prior art. Further, there is a need for new methods of generating specific cell types for scientific use. In this regard, the present invention fulfills this need.